For example, Patent Document 1 discloses a laser pulse generating apparatus for feeding a portion of emission light back to a semiconductor laser by using a polarization maintaining optical fiber.
Also, for example, Non-Patent Document 1 discloses an accurate measurement method of OFDR (Optical Frequency Domain Reflectometry) using an optical feedback path length where polarization is maintained by using a polarization maintaining FBG (Fiber Bragg Grading).
[Patent Document 1] Japanese Patent Laid-Open No. 2007-35661 [Non-Patent Document 1] Omichi et al., “Polarization Division Multiplexing Measurement of Optical Frequency Domain Reflectometry Using Polarization Maintaining Fiber Bragg Grating” Proceedings 1 of the 2008 IEICE General Conference, Kitakyushu, C-3-78, Mar. 18 to 21, 2008